The present invention relates to gearboxes, and, in particular, to a deoiler portion of a gearbox.
A typical gas turbine engine for an aircraft is coupled to a shaft that drives other shafts via a connection to a gearbox. As the air flows through the gearbox housing, a certain amount of oil naturally becomes entrained in the air. For instance, bearing compartments in the turbine can be vented into the gearbox and increase the amount of oil in the air in the gearbox. For a number of reasons, it is desirable that this oil be separated from the air before the air is vented from the gearbox.
In order to separate the oil from the air, a deoiler is included in the gearbox. In general, the deoiler includes a separator unit that utilizes centrifugal forces to separate the heavier oil from the lighter air. In some cases, the deoiler includes a shaft to which the separator unit is attached and that includes an outlet through which clean air can be exhausted to the environment.
When the engine is driving components in the gearbox (e.g., the deoiler), pressures greater than atmospheric build up within the gearbox and, due to the high speed rotating gears within the gearbox, oil from the gearbox itself can become entrained in the air in chamber. As mentioned above, oil can also be introduced from the bearing compartments due to air that leaks into the bearing compartments from the higher-pressure sections of the engine (e.g., compressors and turbines). It is often desirable to minimize the pressure in the gearbox and bearing compartments to help balance the pressure forces on the seals to avoid blowing engine lubricating oil out of the bearing compartments into the lower pressure sections of the compressor, or turbine. For this reason a low pressure drop across the deoiler in general and the separating unit in particular is usually desired as this pressure drop biases the bearing compartment and gearbox pressure upward. That is, if there is a large pressure drop across the separating unit, the pressure in the gearbox must be increased to drive air into it. It is also advantageous to minimize the size (envelope) and weight of the separating unit. However, to achieve the desired pressure drop performance, the size is often increased beyond the size needed to obtain the desired air-oil separation.